Adrenal/thyroid hormones Flashcards
(17 cards)
zones of the adrenal cortex
zona glomerulosa
zona fasciculata
zona reticularis
zona glomerulosa
produces aldosterone
regulated by angiotensin II and potassium concentrations
zona fasciculata
(cells arranged in chords)
produces cortisol
regulated by ACTH (adrenocorticotropic hormone)
zona reticularis
(irregular arrangement of cells)
produces androgens
regulated by ACTH and other factors
cortisol
- type
- area of synthesis
- receptor
- transportation
steroid hormones
produced by zona fasicularis
targets nuclear (II) receptors to alter gene expression
transported in plasma bound to corticotropic-binding globulin
cortisol regulation
hypothalamus releases CRH, pituitary releases ACTH, inducing cortisol release
cortisol has negative feedback on the hypothalamus and pituitary, as well as inflammatory responses
more CRH, ACTH and cortisol released in the mornings
cortisol role in digestion
maintenance of blood glucose during states of fasting
- important for maintaining glucose levels in the brain
- antagonistic to insulin (initiated gluconeogenesis)
cortisol role in circulation
induces vasocontriction
increases Na+/water reabsorption and K+ excretion (increase in blood pressure)
therapeutic uses of corticosteroid drugs
mimics cortisol
used for hormone replacement
used for anti-inflammatories and immunosuppression
- may lead to zona fascicularis atrophy
calcitonin
secreted by parafollicular cells of the thyroid gland
promotes Ca2+ deposition from bone
thyroid hormones
- type
- area of synthesis
- transportation
- function
act as steroid hormones
produced by colloid filled follicle cells of the thyroid composed of thyroglobulin
travel bound to plasma proteins globulin, transthyretin and albumin
T3 = triiodothyronine
T4 = thyroxine (converted to T3)
increase basal metabolic rate
thyroid hormone synthesis
requires iodine for synthesis, is added to tyrosine
1. in the thyroid follicle lumen, where thyroglobulin has been exocytosed, thyroglobulin is iodised and conjugated
2. iodised thyroglobulin is proteolysed to from T3/T4
3. T3/T4 released into blood
thyroid hormone mode of action
act on nuclear receptors (II)
- after entering a target cell, T4 is converted into T3
T3 is transported into the nucleus to bind target sequences
results in initiation of transcription/formation of mRNAs
thyroid hormone regulation
hypothalamus releases TRH (thyrotropin releasing hormone)
pituitary releases TSH
thyroid hormone stimulated to produce T3/T4
T3/T4 have negative feedback on hypothalamus and pituitary
synthesis of thyroglobulin
synthesised through the ER and golgi of follicle cells, then exocytosed into thyroid follicle lumen
congenital hypothyroidism
inadequate thyroid hormone in infants
can cause:
- developmental delays
- learning difficulties
- short stature
- reduced muscle tone
treated by: HRT using levothyroxine
levothyroxine
synthetic T4 (pro-drug)
converted to T3 in the body
